The Internet has professional image banks which provide images for use. These images are often marked, either openly or steganographically, so that their use can be monitored and charged for. Furthermore unauthorized use can be identified. Aside from professional image banks, many rights holders post images on the Internet whose further distribution they would like to control.
While some protection is provided when images are copied and used directly, most image protection systems fail because their protection scheme can be easily removed from the image or can be easily broken if an image is cropped or partially modified. In addition, there is no known protection system if say the image is printed and then scanned back into a new digital image. Furthermore images provided by newspapers or magazines may also be scanned and then posted on the Internet.
Thus some image comparison systems are provided which are able to match an image for different versions of the same image. However these systems are also not very good at finding redigitized versions of images, and are particularly vulnerable if the image has been cropped, flipped, rotated, the color balance has been changed and/or if other distortions have been applied.
Aside from identifying usage of an image for control or charging purposes, it is also desirable to be able to find images to monitor popularity, for marketing, or for numerous other purposes